The present invention relates to a camera, particularly to a camera including an optical system for condensing picture rays onto a light-receiving surface of a solid state image pickup device (CCD) to thereby perform imaging.
CCD cameras using solid state image pickup devices, for example, those disclosed in Japanese Patent Nos. 3277974 and 3297946 have been widely used. Generally, a CCD type solid state image pickup device has a configuration in which light receiving devices for constituting pixels are arranged in a matrix, signals obtained by photo-electric conversion at each light receiving device are read out to a vertical register provided in correspondence with each vertical column of the light receiving devices, the signals are transferred in the vertical direction by the vertical register, the signals are transferred in the horizontal direction by a horizontal transfer register, the signals are converted into voltages by an output unit such as an FDA, and the voltages are outputted to the exterior of the camera.
The cameras using the CCD as above are used not only as still cameras and video cameras but also as cameras which are mounted, for example, to an outside portion of a vehicle body of an automobile or in a compartment of an automobile.
FIG. 13 shows one example of such an automotive camera, in which a CCD 3 is mounted on a substrate 2 disposed in a casing 1, a lens-barrel 5 is disposed on the front side of the CCD 3, and picture rays are condensed onto a light receiving surface of the CCD 3 by lenses 6, 7, 8 and 9 held in the inside of the lens-barrel 5, to form an image. In addition, an opening on the front side of the lens 6 and on the front side of the casing 1 is covered with a protective plate 10.
Such an automotive camera according to the related art has the defect of generation of dewing on the inside surface of the protective plate. Specifically, as shown in FIG. 13, the lenses 6 to 9 are provided in the inside of the camera, and the protective plate 10 composed of a glass or plastic transparent plate is disposed on the front side thereof, so that a plurality of air layers are not present between the outside air and the air layer inside the camera, the temperature difference or temperature gradient between the outside air and the inside of the protective plate 10 is therefore enlarged, and, since the capacity of air inside the camera which makes contact with the protective plate 10 is large, dewing is liable to occur on the inside surface of the protective plate 10.
In view of this problem, as shown in FIG. 14, a glass heater 13 formed by vapor deposition of a metal, for example, is provided on the outer peripheral side of the protective plate 10, and an electric current is supplied to the glass heater 13 from a substrate 2 through lead wires 14, to thereby warm up the protective plate 10 through the glass heater 13. This configuration makes it possible to prevent the surface temperature of the protective plate 10 from being lowered and to prevent the dewing from occurring. However, this leads to an increase in cost due to the glass heater 13, or an increase in electric power consumption due to the power consumption by the glass heater 13, and the rise in the temperature inside the camera produces bad influences on the electric component parts, particularly semiconductor devices inclusive of the CCD 3, which are present inside the camera.
FIG. 15 shows another measure for preventing the dewing. Here, a moisture absorbent 15 such as silica gel is disposed at a predetermined position inside a casing 1, whereby the humidity inside the camera is lowered so as to prevent the generation of dewing. In this case, however, there is the problem that the moisture absorbed into the moisture absorbent as time passes is discharged as water vapor upon a temperature rise due to a camera operation, with the result of dewing, or that the moisture absorbent generates dust or debris. Furthermore, the moisture absorbent 15 leads to an increase in cost and to the need to secure a space for arranging the moisture absorbent 15.